This invention relates to a felt needle to be fastened to a needle board and is of the type which has an elongated needle body that includes a clamping part and a working part which is provided with hooks along its length. The clamping part has a larger diameter than the working part. The felt needle further has a transitional part formed between the working part and the clamping part. The transitional part comprises a region whose diameter decreases from the size of the clamping part diameter to the size of the working part diameter.
For the production of felt, loose fibers that are arranged in a random order one above the other are guided through a machine, between a stripper plate having many holes and a base plate, which is also provided with holes. This fiber blend is repeatedly punctured with a larger number of special needles (felt needles). In the process, these felt needles cause a mutual bonding of the fibers, so that the fiber band gradually becomes more compact and, in the final analysis, a tight felt is produced. In addition to natural fibers and synthetic fibers, recycled fibers are also used. However, these generally have a higher tendency to adhere to the needles and form deposits.
Deposits are formed following a certain period of time during which the feltproducing machine is in operation. The deposits can accumulate on the needles, such that the needles can no longer penetrate the holes in the stripper plate. These deposits cause needle breaks and loss of production. As soon as the depositing process starts, the flow of air between the needles is negatively influenced, thereby causing the deposits to build up even faster. In order to clean the needles, the production must be interrupted. Needle breaks frequently occur during the cleaning.
The material is compacted during the needle-punching process. At the beginning, meaning prior to the needle-punching process, the material is relatively loose and voluminous. Once the needle with its shank region or the intermediate region penetrates the material, it produces holes with the diameter of the shank or the intermediate section, which is larger than the diameter of the working part. This results in a poor surface quality of the felt.
Felt needles with a long, straight shank are known from the German Patent 1760440 C3. The upper end of the shank is angled so that it can be clamped into a needle board. At the other end, the shank is tapered to form a reduced cross section and is furthermore provided with hooks. This section forms a working part, which is used for felting the fibrous web.
The transition between the working part and the remaining shank that serves as clamping part is relatively steep.
The German Published Patent Application 3704471 A1 discloses a device for needle-punching a mineral fiber web. The felt needles that are fastened to a needle board extend parallel to each other away from the needle board and through corresponding openings in a stripper plate. A gap forms between this plate and a base plate that is also provided with openings for the felt needles. The fibrous web is guided through this gap. The felt needles have a cylindrical shank that is angled at the top and is relatively thick. A section of this shank is held in the needle board. A transition region, which is barely longer than the diameter of the shank region, is formed between the clamping part and the toothed working part.
Deposits can form on the cylindrical shank.
German Published Patent Application 2222881 discloses a forked needle with a toothless working region. This working region is connected via a conical intermediate region to a cylindrical shank. The working part has a smooth finish on the outside and is provided with a mouth-shaped fork only at its free end. Depending on the embodiment, a more or less steep transition region in the form of a cone can be provided.
Forked needles are used for structuring compacted fibrous webs in a subsequent operation. Owing to the smooth, toothless flanks of the working part, they have little tendency to pull out fibers from the fibrous web and to carry these along.
Additional felt needles with toothed working parts are known from the U.S. Pat. No. 3,753,412. A relatively short transition part is arranged between the respectively toothed working part and a cylindrical shank.
Felt needles with toothed working parts have a tendency to accumulate fibers on their shanks, which are pulled from the compacted fiber material. During the needle punching of the fibers, the shank extends partially into the working space between stripper plate and base plate. The fibers pulled out from the material are deposited in the form of fiber rings, which are moved from the relatively narrow working part across the short transition region and onto the cylindrical shank region between needle board and stripper plate. In the process, they are expanded and pulled tight. If these deposits exceed a tolerable measure, the puncturing of the web by the needles is obstructed because the needle board no longer can be moved close enough to the stripper plate. Thus, cleaning actions are required from time to time, depending on the fibrous web material used. Owing to the high number of needles on a needle board, such a cleaning action is time-consuming and arduous.